Hypothermia- Exam 1

Question 1

What is the hypothalamus responsible for?

Answer 1

Vascular regulation (vasoconstriction of skin vessels in cold)
Skeletal Muscle activity (vasodilation of skeletal muscle vascular beds in cold)

Question 2

What does the endocrine system do?

Answer 2

Metabolic regulation

Stress response

Question 3

What system does hypothermia activate?

Answer 3

Endocrine system

Question 4

Hypothalamus triggers ___________ nervous system response (triggered by the cold).

Answer 4

Sympathetic

Question 5

Cold is sensed by what in the skin?

Answer 5

Thermoreceptors

Question 6

What does activation of the endocrine system result in?

Answer 6

Oxygen consumption increases
HR increases
CO increases
BP increases

Question 7

What temperature is mild hypothermia?

Answer 7

32-35 C

Question 8

What temperature is moderate hypothermia?

Answer 8

28-31 C

Question 9

What temperature is deep hypothermia?

Answer 9

18-27 C

Question 10

What temperature is profound hypothermia?

Answer 10

< 18 C

Question 11

Why induce hypothermia?

Answer 11

During bypass it provides degree of orange and organism protection; margin of safety

Question 12

3 Mechanisms of Protection in hypothermia

Answer 12

1. Reduction in metabolic rate and O2 Consumption
2. Preservation of high-energy phosphate stores
3. Reduction of excitatory neurotransmitters release due to ischemia

Question 13

What happens with glutamate during ischemia?

Answer 13

It accumulates, opens calcium channels and activates multiple destructive enzymatic systems

Question 14

Which is longer: safe period of hypothermia CPB or period predicted on the basis of reduced metabolic activity alone?

Answer 14

Safe period of hypothermia CPB

Question 15

What are the general effects of hypothermia?

Answer 15

Allows lower pump flows
Better myocardial protection
less blood trauma (low flow = low damage)
Better overall organ protection

Question 16

What is the cardiac index for 34-37 C?

Answer 16

2.4 L/min/m2

Question 17

What is the cardiac index for 30-34 C?

Answer 17

2.0 L/min/m2

Question 18

What is the cardiac index for 25-30 C?

Answer 18

1.8 L/min/m2

Question 19

What is the cardiac index for 20-18 C?

Answer 19

1.5 L/min/m2

Question 20

What is the cardiac index for 18 C?

Answer 20

1.0 L/min/m2

Question 21

Methods of Hypothermia Induction

Answer 21

Surface cooling (ice)
Surface cooling w. supplementary partial bypass
Core cooling - Total ECC (DHCA, HLFB, HILFB)

Question 22

How is surface cooling related to size?

Answer 22

Inverse effect related to size; small infants less than 5kg

Question 23

When do you use DHCA?

Answer 23

Complex congenital heart defects
operations on the aortic arch
operations where maintenance of venous drainage is difficult

Question 24

What should you do if the arrest period is longer than 60 minutes?

Answer 24

use intermittent arrest with brief periods of hypothermic flow
low-flow hypothermic perfusion is safer than total arrest

Question 25

What are the basic global effects of hypothermia?

Answer 25

Decreased energy More bleeding diminished neuro transmission, receptor function, and protein activity

Question 26

Q10 Principle

Answer 26

relates an increase or decrease in reaction rates to a change in 10 C If Q10=2, a decrease in temperature 10C will result in 50% reduction in reaction rates

Question 27

What is the Q10 value for most physiological rates?

Answer 27

2-3

Question 28

Q10 Range (humans)

Answer 28

``` 1.9-4.2 (mean=2) Organ/tissue variability temperature variability (2.23 at 27-30C) 4.5 at 14-27C ```

Question 29

7 degree C Principle

Answer 29

Every 7C drop in temperature will result in a 50% decrease in oxygen consumption (and demand)

Question 30

How do the levels of hypothermia relate to decrease in oxygen consumption?

Answer 30

Mild: 25% decrease Moderate: 50 % decrease Deep: 75% decrease Profound: 87.5 % decrease

Question 31

At 30C VO2 is what percent of normal?

Answer 31

50% normal

Question 32

At 23C VO2 is what percent of normal?

Answer 32

25% normal

Question 33

What does pH respond to?

Answer 33

Changes in CO2 content, not changes in the CO2 components

Question 34

What does temperature change? (CO2 content or proportion of contents?)

Answer 34

Does not change O2 or CO2 content; just the proprotion of the components (dissolved vs partial pressure)

Question 35

Gas solubility is ______________ related to temperature.

Answer 35

Inversely

Question 36

Equation for gas content in solution

Answer 36

Gas content in solution = pp of gas x solubility

Question 37

Henry's Law

Answer 37

As pressure increases, solubility of gases in liquids increases As temperature increases, solubility of gases in liquids decreases

Question 38

Temperature is _________ related to partial pressure.

Answer 38

Directly

Question 39

Temperature is __________ related to solubility.

Answer 39

Inversely

Question 40

Increased temperature ->_________solubility--> _______ partial pressure

Answer 40

decreased, increased

Question 41

decreased temperature--> __________ solubility --> _______ partial pressure

Answer 41

increased, decreased

Question 42

Recommended rate for cooling?

Answer 42

1C per min

Question 43

Recommended rate for warming?

Answer 43

1C per 3-5 minutes

Question 44

Consequences on warming too fast

Answer 44

development of temp gradients within tissues body cooling after bypass exposure to hyperthermia

Question 45

What are the limitations of rate of cooling/warming?

Answer 45

Water temp of heat exchanger BP and SVR Flow Rate

Question 46

Which temperature gradients do we have to worry about?

Answer 46

Btw heat exchanger and venous blood | btw arterial blood and patient

Question 47

Temperature gradients for adults and peds

Answer 47

Adults: < 10 C Peds: < 8 C

Question 48

Keep arterial pO2 below what?

Answer 48

<200mmHg

Question 49

What could cause hyperthermia?

Answer 49

Time pressure of rewarming Efficiency of heat exchanger (more or less than expected) High water temperatures Perfusionist inattention

Question 50

DHCA Temperature

Answer 50

18-20C

Question 51

How long do we turn off the pump in DHCA?

Answer 51

30-60 minutes

Question 52

What organ is at greatest risk in DHCA?

Answer 52

overall brain function, developmental capacity & IQ

Question 53

What is the safe arrest time for normothermia?

Answer 53

4-5 min | O2 consumption 100%

Question 54

What is the safe arrest time for Moderate hypothermia?

Answer 54

8-10 min | O2 consumption 50%

Question 55

What is the safe arrest time for deep hypothermia?

Answer 55

16-20 min | O2 consumption 25%

Question 56

What is the safe arrest time for profound hypothermia?

Answer 56

32-40 min | o2 consumption 12%

Question 57

DHCA Pro's

Answer 57

Allows exposure reduces metabolic rate and molecule movement cessation of circulation excitatory neurotransmitter reduction

Question 58

DHCA Con's

Answer 58

Neurologic Injury & morbidity BRain is at the most risk >60 min is detrimental >40 min increases risk

Question 59

How would you do a combined approach? (HLFB and HILFB)

Answer 59

DHCA with intermittent low flow bypass for 1-2 minutes every 15-20 minutes

Question 60

How do you increase tolerance of brain to ischemic result?

Answer 60

Thiopental - short acting barbituate | Solumedrol- anti-inflammatory, stabilize cell membranes

Question 61

What is a short acting baribituate to increase tolerance of brain to ischemic insult?

Answer 61

Thiopental

Question 62

What is an anti-inflammatory that stabilizes cell membranes to incresa etolerance of brain to ischemic insult?

Answer 62

Solumedrol